If you don't want to sell the engines or give them away, you will need to supply some information and maybe answer some questions.

1)Have you run the engines enough to break them in?

2) Have you adjusted the high speed needle valve correctly? If you not sure how to do this there is an abundance of information on how to do it. Search this site or ask someone with experience to help.

3) Same as 2 for the idle mixture.

4) What is going on when the engine stops? Are you at full throttle and it quits? Are you advancing the throttle from idle to full?

5) Fuel being used? Props?

Put some information here and you will get help.

Good luck.